1. Field of the Invention
The invention relates to a method and means for handling successive sheets to be stacked in a pile.
2. Description of the Prior Art
A stacker station is utilized in a conventional paper making production line to arrange paper sheets into reams. Typically, paper sheets, or clips, issue from a sheeting machine which shears the sheets from a continuous paper web. The sheets are advanced in seriatim fashion along a conveyor system to the stacker, where the sheets are piled.
Good piling requires that the sheets be jogged against a reference. The stacker is provided with a backstop to act as the jogging reference. The problem presented by piling is enabling each successive sheet delivered by the conveyor system to be pushed from the upstream end of the pile over the top of the pile all the way to the backstop without engaging the sheet immediately below it. A sheet which buckles or curls on its way to the backstop will not jog properly and can in some cases be driven over the backstop. In such instances, the ream is ruined and stacker operation may have to be reset, thereby generating loss in production time.
One present method attempting to solve this problem has been to employ corrugating rolls for stiffening the successive sheets. The rolls are mounted at the upstream end of the stacker to give U-shaped corrugations to each sheet passing into the stacker. The U-shaped corrugations give stiffness to the sheet allowing it to be pushed without buckling. However, the height of the corrugations must be accommodated by a differential in elevation between the sheet being delivered and the top of the pile. This differential usually represents a large drop off, which enhances roll-over or buckling as the sheet is applied to the pile.
Another common practice for piling sheets in a stacker has involved air flotation. A typical air flotation device directs air against the undersurface of a sheet as it begins to pass over the pile such that it floats over the pile to jog with the backstop. By the time the sheet reaches the backstop the air pressure beneath the sheet must have dissipated so that the sheet drops onto the pile. However, air directed in this fashion frequently fails to reach the leading edge of the sheet, causing the sheet to buckle before it reaches the backstop. Also, the air has a tendency to hold the tail of the sheet up, making piling and jogging against a reference difficult.
An important object of the present invention is to provide a new and improved method of and means for handling paper sheets to pile in a stacker which will avoid the disadvantages, inefficiencies, shortcomings, and problems inherent in prior arrangements.
A further object of the present invention is to corrugate each sheet being propelled into the stacker for stiffness while, at the same time, permitting a short drop off into the pile.
Another object of the invention is to maintain each sheet level over the pile to a much more reliable degree than heretofore possible.
Still another object of the invention is to transport each sheet to the backstop in a high speed manner with a minimum of machine elements.
A still further object of the invention is to provide structure which accommodates different size sheets in the stacker.
Other and further objects of this invention will be apparent to those skilled in the art from the following description of the annexed sheets of drawings showing a preferred embodiment of the invention.